Objectives of this research proposal are to determine factors which control prolactin concentration in serum of cattle by influencing prolactin release from the pituitary or clearance from serum. To meet the first objective we are conducting experiments with pituitary cells in primary culture and evaluating effects of thyroxine, tri-iodothynmine, estradiol, and testosterone on basal and thyrotropin releasing hormone induced release of prolactin. Complementary studies are being carried out in vivo. Experiments are also designed to determine the effect of tactile and environmental (temperature and light) stimuli on prolactin secretion. Metabolic clearance rate is being quantitated in cattle during various physiological states. In addition, the role of the prepartum surge of prolactin in lactogenesis is being investigated BIBLIOGRAPHIC REFERENCES: McGuffey, R.K., J.W. Thomas and E.M. Convey. 1977. Growth, serum growth hormone, thyroxine, prolactin and insulin in calves after thyrotropin releasing hormone or 3-methyl-thyrotropin releasing hormone. J. Animal Sci. 44:422, 1977. Beck, N.F.G. and Tucker, H.A. Relationships between radioimmunoassay estimates of alpha lactalbumin and prolactin in bovine skim milk. J. Diary Sci., 60:542, 1977.